This invention relates to an active ray-curable composition which can be cured by an active energy ray such as ultraviolet ray (UV), electron beams (EB) or radioactive rays, and to an optical recording medium having a cured product of the composition as an adhesive layer, such as an optical recording disc or an optical memory card.
In the prior art, an optical disc is produced by bonding a recording layer formed on a substrate to a light-pervious protective material by means of a photocuring agent. Preferably, the photocuring agent used for this purpose should be bondable within a short period of time, and be free from components which may adversely affect the recording layer. Moreover, it should not impair the optical properties, such as transparency, of the substrate.
Epoxy resin compositions curable by an active energy ray have been known. Many of them, however, have poor adhesion in the early stage of curing, and since their curing time is relatively long, it is impossible to increase the speed of a production line for optical discs. Moreover, many of them have poor adhesion strength in a humid condition.
Substrates made of various resins are known for use in optical recording media. The industry, however, is seeking substrates made of resins which have excellent heat resistance and little shrinkage upon solidification in melt-molding, and long-term dimensional stability under use conditions, particularly little dimensional changes upon moisture absorption in a high-temperature high-humidity condition.